WatermoleculeWater, H2O, H2O, aqua or aq. is the chemical compound of two hydrogen atoms and an oxygen atom. Water freezes at 0 degrees and evaporates at a hundred degrees Celsius.
It is the only substance that can be found on Earth in three forms: solid (ice), liquid (water) and gas (water vapor). One liter of water weighs 1.01 kilograms. Frozen water is 9% lighter, so ice floats on water.
Water moves around the earth in a water cycle of five phases : evaporation, condensation, precipitation, infiltration and surface run-off.
In a period of 100 years a water molecule spends 98 years in the ocean, 20 months as ice, about 2 weeks in lakes and rivers, and less than a week in the atmosphere.

